The demand for multi-story timber buildings is rapidly increasing due to key factors such as lower costs of realization, high level of prefabrication, and growing environmental awareness. This work focuses on evaluating the dynamic properties of two multi-story Cross-Laminated Timber (CLT) buildings. The selected buildings are two identically realized eight-story residential buildings, part of the Kvarter Limnologen in Växjö (Sweden). At approximately 15 years old, Kvarter Limnologen is among the oldest CLT buildings and is entering a new stage in its life cycle.

To evaluate the modal parameters, three sensor layouts were used during ambient vibration tests. In the first configuration, four sensors were placed on the top story to capture preliminary modal parameters. The second layout increased the number of sensors to twelve, alternating across floors to improve the spatial resolution. Finally, a multi-setup approach was adopted to achieve more accurate mode shapes, using a roving accelerometer configuration while keeping the sensors on the top floor as reference.

The results demonstrate that an optimized sensor placement strategy for multi-setup modal testing allows the evaluation of detailed information about the dynamic properties of the two buildings. The current modal properties—natural frequencies, damping ratios, and mode shapes—of the two building were compared with the results obtained a decade ago. The findings provide valuable insights into the long-term behavior and performance of CLT modular structures, supporting the development of effective structural health monitoring methods.

This study presents a comprehensive investigation of the dynamic behavior of a six-story lightweight timber frame building through periodic and continuous ambient vibration tests. Seasonal changes in temperature and relative humidity can influence the dynamic response of timber buildings, by affecting stiffness, strength, and connection properties due to changes in moisture content. Systematic tests were performed from October 2022 until May 2024 to identify natural frequencies, damping ratios, and mode shapes of the building using five battery-driven data acquisition units equipped with 15 uni-axialaccelerometers. Two different only-output frequency and time domain Operational Modal Analysis (OMA) methods were used to evaluate the dynamic properties of the building. Additionally, the building has been continuously monitored with temperature and humidity sensors since its construction. Results obtained from the periodic measurements highlighted the need for a permanent system to capture the transient changes in the modal parameters. A complementary permanent system to record the accelerations at the roof level was installed in May 2024. The modal parameters from in situ measurements were compared with those obtained from the Finite Element (FE) model of the structure. The FE model, calibrated through a multi-stage approach, incorporating non-structural elements, and varying imposed loads, showed good agreement with experimental data. Comparative analysis of the results obtained under different temperature and humidity conditions showed the effect of the environmental conditions on the building dynamics properties, for both periodic and permanent measurements. This study highlights the importance of continuous monitoring and detailed FE modeling in understanding the dynamic properties and long-term structural behavior under varying conditions. This information can be used to ensure that the building meets safety and performance requirements and to identify potential issues that may need to be addressed during the design and maintenance phases.

Timber-concrete composite (TCC) floor systems have gained interest as a sustainable alternative to concrete floors, particularly in applications requiring longer spans than typical timber floor systems. By connecting timber elements to concrete slabs with shear connectors, TCC systems increase the structural stiffness and improve vibrational characteristics while maintaining a reduced carbon footprint. This study investigates the dynamic performance of a 6 m span glued-laminated timber-concrete composite (GLTCC) floor by means of forced vibration testing and finite element (FE) simulations. Experimental results revealed a first natural frequency of 13.25 Hz, surpassing the 8 Hz requirement specified in Eurocode 5, and a damping ratio of 3.34% for the first mode – close to recommended values for TCC floors with a floating screed. The FE model closely predicts the experimentally measured frequencies and mode shapes, demonstrating the validity of the numerical approach. Parametric studies further highlight the importance of support conditions and connection properties. Continuous supports such as walls or sufficiently stiff beams help maintain higher frequencies, while column supports reduce the frequency in certain modes. Enhanced connection stiffness, as achieved by notches, raises the overall dynamic response, whereas less stiff alternatives, such as screws, lead to reduced composite action and lower frequencies. Overall, these findings confirm the effectiveness of GLTCC floor systems for medium-span applications and highlight the need for careful consideration of support conditions and connection details to ensure optimal vibrational performance.

The material and mechanical properties of wood are influenced by the changes in environmental conditions where moisture content and temperature are particularly important. This study presents a detailed analysis of the evolution of the dynamic properties of a six-story lightweight timber frame building in Sweden over a nine-month monitoring period. A permanent monitoring system, consisting of a data acquisition system and three accelerometers, was installed at the roof level in May 2024. The system is recording the building’s accelerations four times per day for a duration of fifteen minutes each session, resulting in approximately one thousand datasets over the monitoring period. Additionally, a monitoring system for environmental data was installed, measuring temperature and humidity at 18 different measurement point within walls and slabs since construction.

A comparative analysis of the results obtained under varying temperature and humidity conditions was able to show the impact of environmental conditions on the building's dynamic properties. Recorded data show that, on the one hand, a decrease in temperature can lead to an increase in natural frequencies, indicating a structural stiffening, while a decrease in humidity and moisture content generally results in a decrease in the natural frequency’s values.

The importance of incorporating environmental factors into broader structural health monitoring schemes of timber structures is crucial, particularly since changes of environmental conditions could mask the influence of structural damage in the building.

Mass timber (MT) slabs are increasingly used in multi-story buildings due to their sustainability and reduced carbon footprint. While MT diaphragms are typically modeled using a rigid diaphragm approach, recent studies highlight the importance of accounting for the flexibility of the panel-to-panel (PPC) connections. This study presents a finite element (FE) modeling approach for four MT diaphragm systems, validated with experimental data from a six-story shake-table test conducted at the University of California, San Diego. Specifically, this extended abstract focuses on nail-laminated timber (NLT) diaphragms, which have limited dynamic characterization data. The FE model, developed using OpenSeesPy, was validated through operational modal analysis (OMA) of ambient vibration tests. The results showed strong correlations between experimental mode shapes and FE predictions, with the second mode demonstrating excellent agreement (mean MAC = 0.99) and the first mode showing good correlation (mean MAC = 0.87). These findings confirm the accuracy of the proposed modeling approach for capturing the out-of-plane dynamic behavior of MT diaphragms. The study underscores the effectiveness of OMA in extracting diaphragm mode shapes and supports the advancement of more precise modeling techniques for dynamic analysis of MT structures.

The current standards need more specific serviceability criteria for Cross-Laminated Timber (CLT) floors since in some cases discrepancies can be observed between the floor in-service performance in reality and those predicted in standards and design codes. This paper presents a series of analyses of a case study in Sweden, which presented higher fundamental frequency in the CLT floors than predicted in Eurocode 5 (EC5). It aims to investigate the effect of non-structural walls on the floor modal parameters through experimental measurements. The authors compared the analytical predictions of the fundamental frequency using the new draft version of EC5 against the corresponding experimental estimations. Using a sensor-roving approach, a dense sensor configuration was adopted to identify the three floors’ modal parameters. Then, different human-induced excitation scenarios were performed to analyze the floor dynamic responses. The results and analysis in this study shed light on the significance of non-structural internal walls on the vibration performance of the CLT floors, a factor not considered in the practical design for serviceability verifications. The study shows that the presence of partition walls can provide a higher stiffness leading to a significant increase in the first fundamental frequency.

 This paper describes the in-situ ambient vibration tests of a lightweight timber frame building, performed in order to obtain its modal properties. Our case study is a six-story lightweight timber frame building in Varberg, Sweden. Five battery-driven wireless data acquisition units with a total of 14 uni-axial accelerometers were used to perform the in-situ measurements. Accelerations along the two horizontal directions were recorded with a duration of approximately 40 minutes. Two different only-output frequency and time domain Operational Modal Analysis (OMA) methods were used to evaluate the dynamic properties of the building. The modal parameters obtained from the in-situ measurements, such as natural frequencies and mode shapes, were compared with the parameters obtained from the Finite Element (FE) model of the structure. To perform a detailed numerical analysis of the light-frame timber building, all lateral-load resisting system components were modelled. The FE model was calibrated in function of the results obtained from the OMA of the building. Based on the obtained results from the calibrated FE model, it was possible to conclude that the non-structural elements have an influence on the global dynamic response of the building.